In general, a content delivery network (CDN) is a network of servers that delivers a Web page to a user based on the geographic locations of the user, the origin server of the Web page and local servers. Within the CDN, copies of the pages of a Web site are stored in local servers called content engines that are dispersed at geographically different locations, caching the contents of the Web page. Content routers in the CDN route user requests to an appropriate content engine. When a user requests a Web page that is part of a CDN, the CDN redirects the request from the originating site's server to a server in the CDN that is closest to the user and delivers the cached content from that closest server. The CDN also communicates with the originating server to deliver any content that has not been previously cached. This service is effective in speeding the delivery of content of Web sites with high traffic and Web sites that have global reach. Typically, the closer the content engine is to the user geographically, the faster the content will be delivered to the user. CDNs can also be configured to provide protection from large surges in traffic.
Content distribution and management (CDM) is the proactive distribution of cachable content from origin servers to content engines at the edges of a network, and the maintenance required in keeping the content fresh.
Content routing directs a user request to the optimal resource within a global network based on user-defined policies such as rules for specific content, availability of content, health or current loads for Web servers or caches, and various other network conditions. Content routing is also referred to as “request redirection.”
Content switching provides a robust front end for Web server farms and cache clusters, performing functions such as local and global load balancing of user requests, and policy-based Web traffic direction based on full visibility of URLs, host tags, cookies and perhaps other content information.
Content edge delivery is a CDN service that caches select content from origin servers and delivers specific content to a requesting user.
The Domain Name System (DNS), also referred to as the Domain Name Service, is an Internet service that translates domain names into IP addresses. The DNS system is its own network. If one DNS server does not know how to translate a particular domain name, it asks another DNS server, and so on, until the correct IP address is returned.
HyperText Transfer Protocol (HTTP) is the underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands. HTTP is called a stateless protocol because each command is executed independently, without any knowledge of the commands coming before it.
A Uniform Resource Locator (URL) is the global address of documents and other resources on the World Wide Web and other networks using similar protocols. The first part of the address indicates what protocol to use, and the second part specifies the IP address or the domain name where the resource is located. For example, the following URL, http://www.test.com/ indicates that the protocol to be used is HTTP and that the address of the resource is www.test.com.
Transmission Control Protocol (TCP) is a network protocol. TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent. Internet Protocol (IP) specifies the format of packets, also called datagrams, and the addressing scheme. The protocols combined as TCP/IP establish a connection between two hosts so that the hosts can send messages back and forth for a period of time.
The Web Cache Communication Protocol (WCCP), developed by Cisco Systems, of San Jose, Calif., specifies interactions between one or more routers (or Layer 3 switches) and one or more web-caches. The purpose of the interaction is to establish and maintain the transparent redirection of selected types of traffic flowing through a group of routers. The selected traffic is redirected to a group of web-caches with the aim of optimizing resource usage and lowering response times.
File Transfer Protocol (ftp) is the Internet protocol for transferring files.
Network File System (NFS) is a client/server application designed by Sun Microsystems that allows all network users to access shared files stored on computers of different types. NFS provides access to shared files through an interface called the Virtual File System (VFS) that runs on top of TCP/IP. Users can manipulate shared files as if the files were stored locally on the user's own hard disk. With NFS, computers connected to a network operate as clients while accessing remote files, and as servers while providing remote users access to local shared files.
Common Internet File System (CIFS) defines a standard for remote file access. CIFS, like NFS, enables users with different platforms and computers to share files without having to install new software. CIFS, like NFS, can run over TCP/IP but it uses the server message block (SMB) protocol found in Microsoft Windows for file and printer access. CIFS and NFS are used by many applications, including Web browsers, to open and operate on files. Implementations of CIFS and NFS generally provide better support for file access control, file attributes, directory operations, file modifications, and random I/O access patterns in comparison to HTTP.
There are CDN systems that use content routing involving DNS and HTTP messages to route a client's request for web content to a preferred server that will fulfill the client request. There are distributed file system implementations in which clients communicate with a server, and that server complies with a distributed file cache coherency protocol to implement a multi-replica file system, along with one or more other servers that may store the same files. Examples of current distributed file systems include the Andrew File System (AFS) available from the Andrew Consortium at the School of Computer Science at Carnegie Mellon University in Pittsburgh, Pa. and Coda, also developed at Carnegie Mellon University.
Current technology is able to use WCCP to capture DNS and HTTP requests traveling through a network near a particular content engine, and (at the cost of processing 100% of such requests) to process some of those requests locally.